JPS5837030B2 - Coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating an article with a flowing powder material by electrostatic force.

Conventional methods for coating using electrostatic force include the commonly-called electrostatic dynamic dipping method and electrostatic spraying method.

This electrostatic dynamic dipping method involves applying a high voltage through electrodes in a fluidized bath, placing a grounded article on top of a diluted layer of powdered material that is being fluidized by compressed air, and coating it using electrostatic force. This is a method consisting of:

In this electrostatic dynamic dipping method, for example: (1) If a thick film is required to deposit the powder material on the article with an upper dilute layer of flowing powder material, the deposition takes a long time.

■ The voltage applied to the powder substance is a high voltage (for example, 11C
60 to 100 kV), which is very dangerous.

■ A large amount of compressed air is applied to the powder in the fluidized tank to make it flow violently, so a device is required to collect the scattered powder, and the fluidized tank must be sealed each time it is deposited, which takes time to open and close. The efficiency (productivity) for adhesion is low.

(2) If a large amount of powder material is deposited to obtain a thick film, the powder material may smudge or fall off the surface of the article.

In addition, with respect to articles made of composite materials, depending on the type of material, some parts may be difficult to adhere to, and uneven coating may occur.

Although it is possible to apply intermittent shocks to the coating after it has been deposited to prevent it from falling off, in this case localized shedding tends to occur and it is difficult to obtain a smooth coating.

■ In order to improve the fluidity and uniformity of adhesion of the powder material in the fluidized tank, it is necessary to narrow the particle size distribution during the production of the powder material.

There is a drawback.

As a result of intensive research to improve the above-mentioned drawbacks, the present inventors immersed an article in a highly concentrated powder substance that was made to flow weakly with compressed air and applied a voltage with an electrode, and then gave it a rocking effect. ■ Compared to the conventional method of attaching a powder substance to an article with a thin upper layer of powder substance, since the article is immersed in a highly concentrated powder substance, the powder substance is Deposition time is significantly shortened and deposition productivity is greatly improved.

■ No dust is generated because the powder material is made to flow weakly, so there is no need for dust countermeasures such as collection of the powder material.

■ There is no need to take the trouble of narrowly adjusting the particle size distribution of powdered materials.

- The appearance of the coating film after baking is excellent because there is little uneven adhesion of the powder substance and there is no phenomenon of peeling or falling off.

We have discovered an effective coating method.

Regarding (2), the inventors believe that by shaking the article, the chances of contact between the article and the powder substance are further increased, so that the powder substance adheres closely, and this effect was obtained. There is.

The present invention will be explained in more detail.

The coating method of the present invention involves weakly fluidizing the powder material with compressed air, applying a voltage to the powder material through electrodes, immersing the article in the powder material at a high concentration with or without pretreatment, and The basic method is to apply a powder substance to the article while shaking it.

The rocking mentioned here does not necessarily have to be applied continuously, but may be an intermittent smooth movement.

The type of rocking is to make the movement of the article reciprocate on the same spatial plane as much as possible.

If this item is moved in such a way that it reciprocates on the same spatial plane with significant deviations,
As the mechanism for imparting swing to the article becomes more complex, the effect of imparting the swing becomes less obvious.

In general, it is often possible to achieve a goal by swinging it like a pendulum.

Next, the magnitude of the vibration varies depending on the type, material, shape, etc. of the article to which the powder substance is attached, or the type, properties, and adhesion conditions of the flowing powder substance, but for example, when it is applied to small parts such as electronic parts, When applying a powder material such as epoxy resin powder coating for insulation, the period is 0.
It is preferable that the amplitude is in the range of 10 to 300 mm for 1 to 3 seconds, and it also prevents the occurrence of slippage and shedding phenomena of loose powder materials in a well-balanced manner, and further improves the uniformity of the coating film. For this reason, even more favorable results are obtained when the period is in the range of 0.2 to 2 seconds and the amplitude is in the range of 30 to 100 dishes.

Further, this oscillation occurs between the time when the article is in the flowing powder substance atmosphere and until uniform adhesion is obtained, and gives oscillation to the article.

Also, it is often possible to achieve this goal by applying agitation only while the article is in an atmosphere of flowing powder material.

In the coating method of the present invention, the fluid state of the powder material allows the powder material to be adhered to the article in a state where the fluid concentration of the powder material is very high.

Furthermore, safety is improved by lowering the applied voltage for generating electrostatic force.

That is, although it goes without saying that the applied voltage differs depending on the type of powder material, usually D. It is preferable to charge using a relatively low voltage of CLO to 50 kV.

The coating method of the present invention is a method in which the article is immersed to the inside in a weakly fluid powder substance, and a thick film can be obtained with a single deposition operation, and since the coating method is weakly fluid, no dust is generated. No collection device is required.

This weak flow refers to the apparent volume ratio of the powder material used, which varies depending on its properties and type, but is generally 1.0.
It refers to a state where the increase is 5 to 1.5 times, more preferably 1.1 to 1.2 times.

To explain the apparent volume ratio described here, the apparent volume ratio is defined as the normal apparent volume of the powder substance being 1,
It is the increase in apparent volume when a powder substance is fluidized with compressed air.

Furthermore, in the method of the present invention, by pre-treating the article, it is possible to exhibit the effects of the present invention to a greater extent than when the article is not treated.

Pretreatment of an article as used herein refers to preheating the article, prewetting the article with a liquid substance, and using a combination of preheating and wetting the article with a liquid substance.

Preheating means that in contrast to the known fluidized dipping method that does not use static electricity, which requires preheating the article to a temperature above the melting point of the powder material, the method of the present invention does not necessarily require preheating the product to a temperature above the melting point of the powder material. The effect is further improved even with a weak preheating.

The liquid substance of the present invention includes thermoplastic resins, thermosetting resins,
Contains conventional liquid substances such as plasticizers, solvents, inorganics, or mixtures of at least two of these.

This liquid substance is used by impregnating or applying it to the article,
It is often preferable to use it to improve film properties such as improved adhesion, improved water resistance, and prevention of pinholes.

Powder materials that can be used in the present invention include all powder materials that can be coated onto articles.

For example, synthetic organic compounds such as epoxy resin, acrylic resin, polyester, polyurethane, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide, ethylene vinyl acetate copolymer resin, polyvinyl butyral, phenol resin, amine resin, fluororesin, synthetic rubber, etc. , natural organic compounds such as starch and rosin, mixtures containing these as main ingredients and inorganic compounds, and further inorganic compounds such as frits.

The articles to which the present invention is applied are various articles requiring a surface coating.

Examples include electronic parts, electrical parts, mechanical parts and their products, building materials, industrial products, daily necessities, and ceramic products.

Hereinafter, the present invention will be specifically explained with reference to Examples.

However, in the coating method of the present invention, after attaching the powder substance to the article, a normal post-processing operation such as heating is performed to coat the article.
Also included is obtaining a coating.

Incidentally, the swinging motion need not only be applied directly to the article, but may also be applied indirectly to the article through a part of the device that supports the article.

Example 1 A lead wire welded polypropylene film capacitor element was used as an article, and a swing consisting of a pendulum type motion with a period of 0.5 seconds and an amplitude of 40 rIL 1 ft was applied to it.

In the fluidized tank, compressed air makes the apparent volume 1.15 times the normal apparent volume, and the epoxy resin powder coating for electrical insulation (manufactured by Sumitomo Durez ■, "Sumilight Resin") is gently flowing. JPR-52102) was subjected to shaking and the grounded element was immersed.

D. to powder coating. A voltage of C 5 0 kV was applied to charge the element, and the powder coating was applied to the element for 4 seconds by electrostatic force, and then the element was pulled up for 0.5 seconds while being further rocked.

As a result, an element was obtained in which the powder coating was uniformly adhered to all parts.

Next, the element to which the powder coating was applied was baked in an oven at a temperature of 90°C for 2 hours, and as a result, the film thickness on the entire surface was approximately 0. It had an excellent coating film with a thickness of 4 mm and no uneven coating.

Example 2 A lead wire welding type polypropylene film capacitor element was prepared in advance by adding 100 parts by weight of a liquid epoxy resin (manufactured by Shell Chemical ■, "Epicote J828") and 90 parts by weight of a liquid acid anhydride (manufactured by Hitachi Chemical ■, methylnadzic acid anhydride). The surface was wetted with a liquid substance consisting of a mixed solution.

After powder coating was applied to the device using the same procedure as described in Example 1, baking was performed.

As a result, the film thickness over the entire surface was approximately 0. The thickness was 6 mm, and the uniformity was extremely excellent.

In this example, compared to Example 1, the thickness of the deposited film was significantly reduced at the same deposition time.

Example 3 Regarding a lead wire welding type polypropylene film capacitor element, powder coating was applied to the element preheated to 60°C by the same procedure as described in Example 1, and then
I did the baking.

As a result, the film thickness over the entire surface was approximately 0. 4 5 WL
m, and had extremely excellent uniformity.

In this example, an effect was observed in that the thickness of the deposited film was larger than that in Example 1 at the same deposition time.

Comparative Example A lead wire welding type polypropylene film capacitor element was placed on top of an electrically insulating epoxy resin powder coating (Sumitomo Durez ■, "Sumilight Resin" PR-52102) that was being violently fluidized by compressed air in a fluidized fluid tank. It was kept in a dilute layer.

D. to powder coating. C. A voltage of 70 kV was applied to charge the element, and the powder coating was applied to the element for 15 seconds by electrostatic force.

Next, the element to which the powder coating was applied was baked in a furnace at a temperature of 90°C for 2 hours, resulting in an average film thickness of about 0. It had a coating of 4 mm.

However, the upper surface of the element becomes a thicker film than that of the powder coating, and the average film thickness is about 0.4 mm at a maximum of ±O. It had a variation of 15.

Furthermore, the powder coating on the lower surface of the element often fell off locally due to a slight impact generated during the coating operation, and the coating film often lacked smoothness.

In this comparative example, the above-mentioned falling-off phenomenon occurred due to a slight impact, but such a phenomenon did not occur in the cases of each of the above-mentioned Examples.

Further, compared to the case of Example 1, it took a longer time to deposit a powder coating of the same weight (same film thickness), and the coating film smoothness was 6 points lower.

Claims (1)

[Scope of Claims] 1. An article is pretreated or immersed without pretreatment in a highly concentrated powder substance that is weakly fluidized by compressed air and a voltage is applied by an electrode, and the article is shaken. 1. A method of coating an article, comprising applying a powder substance to the article while applying motion. 2. A method according to claim 1, characterized in that the agitation is applied to the article while it is in the highly concentrated powder material atmosphere until uniform adhesion is obtained. 3. The method according to claim 1 or 2, wherein the swinging motion is applied so that the article moves back and forth on the same plane in space. 4. The method according to claim 1, 2, or 3, wherein the apparent volume of the flowing powder material is 1.05 to 1.5 times the normal apparent volume. 5. The method according to claim 1, 2, 3 or 4, characterized in that the article is pre-wetted with a liquid substance and then the powder substance is applied. 6. A method according to claim 1, 2, 3 or 4, characterized in that the article is pre-wetted with a liquid substance and then preheated to deposit the powder substance. 7. A method according to claim 1, 2, 3 or 4, characterized in that the powder substance is applied after preheating the article. 8. Claim 1, characterized in that after preheating the article, it is wetted with a liquid substance and a powder substance is applied thereto;
The method according to paragraph 2, paragraph 3, or paragraph 4.